CD38 is a multifunctional protein having function in receptor-mediated adhesion and signaling, as well as mediating calcium mobilization via its ecto-enzymatic activity catalyzing formation of cyclic ADP-ribose (cADPR) and ADPR. CD38 mediates cytokine secretion and activation and proliferation of lymphocytes (Funaro et al., J Immunol 145:2390-6, 1990; Terhorst et al., Cell 771-80, 1981; Guse et al., Nature 398:70-3, 1999). CD38, via its NAD glycohydrolase activity, also regulates extracellular NAD+ levels, which have been implicated in modulating the regulatory T-cell compartment (Adriouch et al., 14:1284-92, 2012; Chiarugi et al., Nature Reviews 12:741-52, 2012). In addition to signaling via Ca2+, CD38 signaling occurs via cross-talk with antigen-receptor complexes on T and B cells or other types of receptor complexes, e.g., MHC molecules, involving CD38 in several cellular responses, but also in switching and secretion of IgG1.
CD38 is a type II transmembrane glycoprotein expressed on hemopoietic cells such as medullary thymocytes, activated T- and B-cells, resting NK cells and monocytes, lymph node germinal center lymphoblasts, plasma B cells, intrafollicular cells and dendritic cells. A portion of normal bone marrow cells, particular precursor cells as well as umbilical cord cells are CD38-positive. In addition to lymphoid precursor cells, CD38 is expressed on erythrocytes and on platelets, and expression is also found in some solid tissues such as gut, brain, prostate, bone, and pancreas. Mature resting T- and B-cells express limited to no surface CD38.
CD38 is also expressed in a variety of malignant hematological diseases, including multiple myeloma, leukemias and lymphomas, such as B-cell chronic lymphocytic leukemia, T- and B-cell acute lymphocytic leukemia, Waldenstrom macroglobulinemia, primary systemic amyloidosis, mantle-cell lymphoma, pro-lymphocytic/myelocytic leukemia, acute myeloid leukemia, chronic myeloid leukemia, follicular lymphoma, Burkitt's lymphoma, large granular lymphocytic (LGL) leukemia, NK-cell leukemia and plasma-cell leukemia. Expression of CD38 has been described on epithelial/endothelial cells of different origin, including glandular epithelium in prostate, islet cells in pancreas, ductal epithelium in glands, including parotid gland, bronchial epithelial cells, cells in testis and ovary and tumor epithelium in colorectal adenocarcinoma. Other diseases, where CD38 expression could be involved, include, e.g., broncho-epithelial carcinomas of the lung, breast cancer (evolving from malignant proliferation of epithelial lining in ducts and lobules of the breast), pancreatic tumors, evolving from the β-cells (insulinomas), tumors evolving from epithelium in the gut (e.g. adenocarcinoma and squamous cell carcinoma), carcinoma in the prostate gland, and seminomas in testis and ovarian cancers. In the central nervous system, neuroblastomas express CD38.
Acute lymphoblastic leukemia (ALL) is characterized by impaired early lymphoid development and is classified as either B-cell or T-cell ALL. Buriktt's lymphoma (“Mature B cell lymphoma”) is also classified as ALL. Incidence of ALL is about 6000 new cases per year, or approximately 1 in 50,000. Both genetic and environmental factors contribute to ALL, with several chromosomal rearrangement and submicroscopic genetic alterations identified (Inaba et al., Lancet 381:1943-55, 2013). Overall response rates to therapy in children having ALL is about 80%, and about 45%-60% in adults with ALL. Unfortunately, prognosis in relapsed ALL is poor.
Therefore, there remains a need for effective treatments for ALL.